(1) Field of the Invention
The present invention relates to a hydraulic control apparatus for marine reversing gear assembly for watercraft, and more particularly to a hydraulic control apparatus for trolling.
(2) Description of the Related Art
In recent years, the engine speeds for small watercraft such as small fishing boats, recreational fishing boats, and the like have increased (for example, to a speed of 4,000 rpm or higher). When traveling at very low speeds, such as when trolling or the like, the engine is required to run at low speed; however, driving a high-speed-type engine at low speed may cause hunting or engine stalling, making it impossible to drive the engine at the desired low speed. For this reason, the engine is driven at low speed by causing hydraulic clutches located between the engine and the output shaft to slip relative to each other when engaged (i.e., in a half-clutch condition). As an alternative, the provision of a multistage transmission or a continuously variable transmission to cover the range from low to high speeds can also be considered. The provision of such a transmission, however, increases the size of the control apparatus, and also increases the cost, and is therefore not suitable for small watercraft.
For reasons such as those set forth above, hydraulic clutch-type marine reversing gear assembly for watercraft have, for example, a pressure reducing valve referred to as a low-speed valve in a circuit for supplying a working oil to the hydraulic clutches, in order to travel at very low speeds, e.g., when trolling. This allows the pilot pressure to the low-speed valve to be controlled by a proportional electromagnetic valve that interlocks with a trolling lever, so as to control the number of revolutions of the propeller shaft to follow the instruction value from the trolling lever. On the other hand, the supply of the working oil to the proportional electromagnetic valve is turned on and off by an electromagnetic switching valve referred to as a direct-coupled electromagnetic valve. When the proportional electromagnetic valve is turned off, the low-speed valve is fully opened to cause the hydraulic clutches to be in full engagement, such that switching is performed between trolling and normal traveling. A hydraulic control apparatus for marine reversing gear assembly for watercraft as described above is disclosed in, for example, Japanese Unexamined Utility Model Publication No. 6-78637.
However, in order to control the proportional electromagnetic valve and direct-coupled electromagnetic valve simultaneously, it is necessary to execute the timing for switching the direct-coupled electromagnetic valve by using a complicated control program (software). This increases the cost of the control system that includes the controller.
Accordingly, an object of the present invention is to provide a hydraulic control apparatus for marine reversing gear assembly for watercraft by replacing a direct-coupled electromagnetic valve with a mechanical switching valve that does not require electronic control, thereby obviating the need for complicated electronic control to reduce the cost.